Composite materials in which a carbon material is blended with a polymer material, such as a resin or rubber, are conventionally used as materials having excellent electrical conductivity and mechanical characteristics. Moreover, in recent years, carbon nanotubes (hereinafter also referred to as “CNTs”) have been attracting interest as a carbon material that is highly effective for improving electrical conductivity and mechanical characteristics. Among such CNTs, there is particular interest in the use single-walled carbon nanotubes (hereinafter also referred to as “single-walled CNTs”) as a carbon material for a composite material. This is because single-walled CNTs are a fibrous conductive filler that exhibits high electrical conductivity and can favorably improve electrical conductivity and mechanical characteristics of composite materials even when the blending amount thereof is small.
In order to favorably improve electrical conductivity and mechanical characteristics of a composite material, it is necessary to homogeneously disperse a carbon material, such as CNTs, in a matrix of a polymer material. A technique has been proposed in which a composite material of CNTs homogeneously dispersed in a matrix of a polymer material is obtained by preparing a composite material composition through mixing of the polymer material and a carbon nanotube dispersion liquid in which the CNTs are homogeneously dispersed in a dispersion medium, and then using the composite material composition to produce the composite material.
However, CNTs such as single-walled CNTs tend to readily aggregate and become entangled with one another. Consequently, in production of composite materials using CNTs as a carbon material, there is demand for a technique that enables efficient production of a carbon nanotube dispersion liquid of homogeneously dispersed CNTs.
In response to this demand, PTL 1 for example proposes a technique in which shear force, shock waves, cavitation, or the like is used to break CNTs that are coarsely dispersed in a dispersion medium in order to obtain a carbon nanotube dispersion liquid in which the broken CNTs are highly dispersed. Moreover, PTL 2 for example proposes a technique in which aggregated CNTs in a dispersion medium are untangled and severed using an ultrasonic homogenizer in order to obtain a carbon nanotube dispersion liquid in which the CNTs are highly dispersed. Furthermore, PTLs 3 and 4 for example propose a technique in which a coarse dispersion liquid of CNTs coarsely dispersed in a dispersion medium is subjected to a plurality of cycles of dispersing treatment at a fixed treatment pressure using a jet mill in order to obtain a carbon nanotube dispersion liquid in which the CNTs are favorably dispersed, while also suppressing damage to the CNTs.